The Transportation Security Administration (TSA), after testing paperless boarding passes at a few airports to make sure they are secure, plans a nationwide expansion in the next year, spokesman Christopher White said.

Alaska Airlines just started using paperless boarding passes at Seattle-Tacoma International Airport and could expand next year to Los Angeles, Anchorage and Portland, Ore., spokeswoman Marianne Lindsey said.

The boarding passes are e-mailed to a passenger's cellphone or PDA and appear on screen as a bar code. At security checkpoints, a TSA screener scans the code with a $1,000 handheld device, which displays a passenger's name and flight information for comparison to a passenger ID. Passengers can still use traditional paper boarding passes.

The TSA requires airlines to add security features to the electronic bar codes to help spot a forged boarding pass. The agency must approve airlines' plans to use paperless boarding passes.

Paperless boarding passes are expanding overseas, too. Last month, Lufthansa began allowing passengers to use the passes on all 1,000 of its daily flights from Germany to other European destinations. Air France, KLM and smaller European airlines also use paperless boarding passes.

"Within two to four years, it's going to be standard across Europe," said Oliver Wagner, a vice president of Lufthansa.

The International Air Transport Association, an airline trade group that has created global criteria for boarding passes, recently added the TSA security requirement to its standard for paperless passes, said Eric Leopold of IATA. "The U.S. is the only country ... that has such a requirement," he said.

Since the TSA first OK'd paperless boarding passes in December, Continental Airlines has started using them at six airports, including Houston Intercontinental and Newark Liberty, and will add Cleveland Hopkins as its seventh airport on Thursday. Northwestern uses them in Indianapolis.